In the 17th century, China used silica sand as a molding material to make castings such as clocks, mirrors, pots and artillery. However, in the early days, most of the natural silica sand containing clay, namely mountain sand and river sand, was used, which had good plasticity and could be directly used to make molds and cores, and was suitable for manual production at that time. After the castings entered the industrial mass production, especially after the molding mechanization, the performance uniformity of this natural silica sand containing clay was poor, and the quality of molding sand was difficult to control, which could not meet the technological requirements. Therefore, a sand factory was started to wash, scrub and select the natural silica sand to obtain various high-quality silica sand. Casting sand

or artificial silica sand made by crushing silica. At the same time, it also expands the use of various non-silica sands. The application and development of resin sand molding core-making technology put forward higher requirements for the quality of foundry sand, such as less fine powder, small specific surface area and low acid consumption. In addition, there are new requirements for the size, shape and particle size distribution of sand particles. Some countries lacking high-quality sand sources have also developed silica sand flotation technology to improve the grade and quality of silica sand.

Edit the basic requirements of this paragraph

Casting sand should meet the following requirements: ① High purity and cleanliness. Taking silica sand as an example, the content of SiO22 _ 2 in cast iron sand should be above 9%, and that in larger steel castings should be above 97%; ② High fire resistance and thermal stability; ③ Suitable particle shape and composition; ④ Not easily wetted by liquid metal; ⑤ Cheap and easy to get.

Edit the particle shape and composition in this section

The particle shape and composition of casting sand have an influence on the properties of molding sand, such as fluidity, compactness, permeability, strength and permeability resistance to liquid metal, and are important indicators of casting sand quality.

Edit the particle shape of this section

There are generally three shapes of casting sand. ① Round sand: the particles are spherical or close to spherical, with smooth surface and no prominent edges and corners. ② Polygonal sand: The particles are polygonal and mostly obtuse. ③ Sharp-angled sand: The particles are sharp-angled with more acute angles. The particle shape of casting sand is generally expressed by angular coefficient (the ratio of actual specific surface area of sand particles to theoretical specific surface area of spherical sand particles). (as shown in the figure)

Edit the particle composition in this section

The particle composition of sand is represented by the screen number. The determination method is to pour the dry sand washed, slimed and dried into a standard screen, and then put it on a sand screen for screening. After screening, the sand remaining on each screen is weighed separately. Usually, the particle composition is represented by the head and tail screen numbers of three adjacent screens with the most concentrated sand particles after screening by the standard screen.

Edit the types and uses of this paragraph

Casting sand can be divided into quartz sand and special sand according to different mineral compositions. Quartz sand is commonly known as silica sand.

edit the silica sand in this section

The main mineral composition is Shi Ying, and the main chemical composition is SiO2. ① Natural silica sand: Because of its different chemical composition and particle size composition, it is used as molding sand and core sand for nonferrous alloy castings, iron castings and small and medium-sized steel castings respectively. ② Selection of natural silica sand: used for molding sand and core sand of various steel castings with organic matter as binder. ③ Artificial silica sand: molding sand and core sand used for precision casting, lining or steel casting.

edit non-siliceous sand in this section

There are many types of non-siliceous sand with different uses. ① Limestone sand: It is crushed from limestone, and the main mineral composition is CaCO3, which is used as molding sand and core sand for steel castings. ② Zirconium sand: The main mineral composition is ZrO _ 2 SiO _ 2, which is used for core sand or sand mold surface sand of large steel castings and alloy steel castings, or its powder is used as coating. ③ Magnesia: The main mineral composition is MgO, which is used for surface sand and core sand of high manganese steel castings, and its powder can be used as coating. ④ Chromite ore: The main mineral composition is chromite FeO·Cr2O3, which is used for surface sand and core sand of large or special steel castings, and its powder can be used as coating. ⑤ corundum sand: The main mineral composition is corundum α-Al2O3, which is used as shell-making material for investment casting and ceramic mold casting. ⑥ Olivine sand: The main mineral composition is olivine (MgFe)2SiO4, which is used as molding sand and core sand for iron castings, nonferrous alloy castings and high manganese steel castings.

editing the resources in this paragraph

There are abundant silica sand resources in nature, but there are not many natural silica sand with high SiO2 content suitable for casting. Since 1951, China has carried out a general survey of foundry sand resources in succession, but it is mainly limited to traffic trunk lines and the vicinity of major industrial cities. The survey results show that China is rich in natural silica sand resources which can be used for casting, and its distribution range is very wide. In Zhelimu League, Inner Mongolia, the natural silica sand reserves reach hundreds of millions of tons, its particle shape is close to circular, and the SiO2 content is about 9%. The sea sand of Jinjiang and Dongshan in Fujian has a SiO2 _ 2 content of 94 ~ 98% and a low silt content, which are all good natural silica sand. Duchang, Xingzi and Yongxiu counties in Jiangxi Province all have a large number of Quaternary fluvial-lacustrine sedimentary silica sand, with a content of about 9%, low iron content, few alkaline oxides and uniform particle SiO2, which is a good lake sand. Guangzhou, Hunan and other places are rich in easily broken weathered sandstone, which can be processed into artificial silica sand, and its SiO2 _ 2 content is above 96%, which can be used for the production of steel castings.